Casting alloy



p 1964 F. G. HAYNES 3,148,054

CASTING ALLOY Filed June 1, 1960 2 Sheets-Sheet 1 FIG! HOURS, LIFE TO RUPTURE 6 29tS.i./8l5C 3 8.0 8.5 90 9.5 IOO FRANK G. HAYNES INVENTOR.

ATTORNEY P 1964 F. G. HAYNES 3,148,054

CASTING ALLOY Filed June 1, 1960 2 Sheets-Sheet 2 FIG. 2

I00 I m '7t.sJ./!O20C m g 5 O m \atsi/saom o F 30 E l 20 {Q 29tS.i./8l5C o I (Ti+A|)% F IG.3

w g 29tsJ./8|5C E 50' .'./|02oc m I E 9.8f.s.i./980C m 30 E l 0'; 20 c: D o a:

FRANK G. HAYNES INVENTOR.

BY Qz.@r- 2 ATTORNEY United States Patent ice 3,148,054 CASTING ALLOY Frank G. Haynes, Kings Heath, Birmingham, England, assignor to The International Nickel Company, Inc., New York, N.Y., a corporation of Delaware Filed June 1, 1960, Ser. No. 33,134 Claims priority, application Great Britain June 8, 1959 2 Claims. (Cl. 75-171) The present invention relates to alloys and, more particularly, to alloys having a nickel-chromium base which in the as-cast state have good resistance to creep at high temperatures and are suitable for use as casting alloys for making articles and parts that are subject in use to stress at high temperatures.

It is well known that such alloys are commonly assessed on the basis of their casting properties and of their behavior in a stress-rupture test at a single temperature, which is generally a high one so that short time tests may be made without recourse to excessively high stresses. In use, however, parts made from the alloys are subjected to a wide range of temperatures and it is desirable that a given composition be the optimum so that over the working temperature range there is achieved a uniformity of properties. One basis of comparison commonly employed is that a stress of 7 long tons per square inch (t.s.i.) at 1020 C., is equivalent to a stress of 9.8 t.s.i. at 980 C. and to a stress of 29 t.s.i. at 815 C. It is desirable and advantageous that the life to rupture of an alloy should not vary greatly under each of these three sets of conditions since this will provide a criterion for the desired uniformity of properties. It is also important that the properties of a casting alloy should be reproducible from heat to heat and little affected by unavoidable variations in casting conditions and chemical composition. A criterion of reproducibility is the standard deviation hereinafter defined.

Frequently, one or other of these conditions is not satisfied and it is unique that an alloy is satisfactory in both respects. The reproducibility of characteristics is particularly important when an alloy is made in commercial quantities to meet a compositional specification having a working range for aluminum and/ or titanium contents. It is well known that in the class of alloys under consideration, these elements are employed as hardeners and that uniform recoveries of these elements in commercial melting practice is very diificult. Since, in commercial practice and especially where scrap is employed in a charge, the total of aluminum plus titanium can vary widely within the limits of a commercial specification, it is highly advantageous to employ an alloy which will exhibit stress-rupture characteristics of the same order despite this unavoidable variation. Although attempts were made to provide a reproducible casting alloy having uniform characteristics, none, as far as I am aware, was entirely successful when carried into practice commercially on an industrial scale.

It has now been discovered that by specially controlling the ratio of titanium to aluminum and the contents of chromium, cobalt, molybdenum, aluminum, titanium, carbon, boron and zirconium in a nickel base casting alloy, good reproducibility and uniformity of stressrupture characteristics in the as-cast state can be provided.

3,148,054 Patented Sept. 8, 1964 It is an object of the present invention to provide casting alloys having in the as-cast state creep properties that give both good reproducibility and uniformity over a range of about 815 C. to about 1020 C.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawing in which:

FIGURE 1 is a graph relating life to rupture in hours to the content of aluminum plus titanium in an alloy not in accordance with the invention;

FIG. 2 depicts another similar graph relating to a different alloy not in accordance with the present invention; and

FIG. 3 shows the relationship of life to rupture in hours and the total of the aluminum and titanium contents in an alloy Within the contemplation of the present invention.

Generally speaking, the present invention contemplates alloys containing from about 13% to about 20% chromium, from about 3% to about 7% cobalt, from about 3% to about 7% molybdenum, from about 1.0% to about 2.8% titanium, from about 4.7% to about 7.5% aluminum, from about 0.05% to about 0.25% carbon, from about 0.003% to about 0.03% boron and from about 0.02% to about 0.07% zirconium, the balance (apart from impurities including incidental elements) being nickel, the ratio of the titanium to the aluminum contents does not exceed about 0.5 and the (Ti+Al) content must lie between about 7 to 9. Advantageously, the Ti/Al ratio is about 0.4 and the Ti-j-Al content is about 7 to 8. The usual impurities and incidental elements such as silicon, iron and manganese can be present without deleteriously affecting the properties of the alloys. Advantageously, the percentages should be low. For example, these elements can be present in amounts up to about 0.2% silicon, 0.5% iron and 0.2% manganese.

In alloys of the present base composition, it is known that titanium and aluminum are the most critical elements from the point of view of rupture strength at high temperature. The present invention is based upon the surprising discovery that under a given setof test conditions an optimum (Ti+Al) content has been found which gives the maximum stress-rupture life and that to achieve the desired uniformity of properties over the whole temperature range, it is desirable that the optimum (Ti+Al) content should be the same at all temperatures within the range of experience.

To illustrate the effect of varying the (Ti+Al) content on the properties at different temperatures, three series of alloys were prepared which (besides titanium and aluminum) had the nominal composition 15% chromium, 5% to 10% cobalt, 5% to 7.5% molybdenum, 0.2% carbon, 0.02% boron and 0.05% zirconium, the balance being nickel. The first two series of alloys had a Ti/Al ratio of 1.1 and 0.6, respectively, and for this reason alone are outside the scope of the invention. The third series which includes the advantageous alloys of the present invention had a Ti/Al ratio of 0.4.

The life-to-rupture characteristics of the three series of alloys are shown in the graphs in FIGURES 1, 2 and 3 of the drawing. Referring now thereto, it is to be noted that in these graphs the life to rupture is plotted as ordinate and the (Ti+Al) as abscissa. The base compositions of the alloys exclusive of titanium and aluminum area-e54 contents upon which these figures are based are set forth in Table I:

It is to be noted from a comparison of the graphs in FIGURES l to 3, that the optimum (Ti-l-Al) content is the same at all three chosen test temperatures in FIG. 3 but that the optimum (Ti-l-Al) contents are widely scattered in the graphs shown in FIGURES 1 and 2. This remarkable coincidence of the optimum (Ti-l-Al) contents as illustrated in FIG. 3 is attributable primarily to the low Ti/Al ratio of the alloys of the present invention. Thus, the alloys of the present invention exhibit in fact an optimum over what might be realistically called the practical working temperature range. The life to rupture shows a minimum sensitivity to the small yet inevitable variations in the titanium and aluminum contents which occur in practice. This provides improved reproducibility in the chosen composition from heat to heat.

As an additional illustration of the improved reproducibility referred to above, two alloys were selected: Alloy A within the scope of the present invention and Alloy B outside it. The composition of Alloys A and B is as follows:

Alloy A:

Chromium percent 15 Cobalt do 5 Molybdenum do 5 Carbon do 0.2 Boron do 0.02 Zirconium do 0.05 Titanium do 2.2 Aluminum do 5.3 Titanium-l-aluminum do 7.5 Titanium/aluminum 0.4 Nickel "percent" Balance Alloy B:

Chromium percent Cobalt do 10 Molybdenum do 5 Carbon do 0.2 Boron do 0.02 Zirconium do 0.05 Titanium d0 3 Aluminum do 5 Titanium-l-aluminum do 8 Titanium/aluminum 0.6 Nickel percent Balance Table H (Alloy A) Within the Scope of the Invention {Ti/Al ratio=0A1 Tempera- Life to Rupture Standard Stress (t.s.i.) ture, C. (hours) Detviatgon 75, 42, 5s, s9, s7, 33

4 T able III (Alloy B) Outside the Invention [Ti/Al ratio:0.6]

Tempera- Life to Rupture Standard Stress (t.s.i.) ture, C. (hours) Deviation (t.s.i.)

The end column of each of these tables sets forth the standard deviation in tons per square inch. The standard deviation, which is the root means square of the deviations of a set of observations from the mean, is a criterion of reproducibility and hence of the uniformity of properties of an alloy and is obtained 'in the following way.

The life to rupture in hours is converted to logarithmic values and the standard deviation of these is calculated from the following formula:

where n is the number of observations;

2 is the symbol for summation of; and

X is the common logarithm of the value of the life to rupture in hours.

The value for S, the standard deviation, is converted from a logarithmic value for time to tons per square inch by reference to the slope of the stress per log time plot for the particular alloy.

It is found that in castings made from alloys having a Ti/Al ratio less than 0.5, the incidence of shrinkage porosity is less than in castings of alloys of higher Ti/Al ratios and this may be one of the reasons for the better reproducibility of properties of castings made from the alloys having a lower Ti/Al ratio. FIG. 3 also shows that at a Ti/Al ratio of 0.4 the properties are very little affected by small compositional changes such as may occure from heat to heat in repetitive production and this again may contribute to the reproducibility of the properties.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, .as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

I claim:

l. A cast alloy having good stress-rupture characteristics at temperatures in the range of about 815 C. to about 1020 C. and exhibiting substantially enhanced characteristics of uniformity and reproducibility over the said temperature range, said alloy consisting, by weight, of about 13% to about 20% chromium, about 3% to about 7% cobalt, about 3% to about 7% molybdenum, about 1.0% to about 2.8% titanium, about 4.7% to about 7.5% aluminum, the sum of the titanium and aluminum being about 7% to 9% and being so correlated that the ratio of the titanium percentage to the aluminum percentage is not greater than 0.4, about 0.05% to about 0.25% carbon, about 0.003% to about 0.03% boron, about 0.02% to about 0.07% zirconium and the balance being essentially nickel, said cast alloy being further characterized by a lesser incidence of shrinkage porosity as a result of the said ratio of titanium to aluminum.

2. A cast alloy having good stress-rupture characteristics at temperatures in the range of about 815 C. to

about 1020 C. and exhibiting substantially enhanced characteristics of uniformity and reproducibility over the said temperature range, said alloy consisting, by weight, of about 15% chromium, about 5% cobalt, about 5% molybdenum, about 2.2% titanium and about 5.3% aluminum to thus give a ratio of titanium to aluminum of about 0.4, about 0.2% canbon, about 0.02% boron, about 0.05% zirconium and the balance being essentially nickel, said cast alloy being further characterized by a lesser incidence of shrinkage porosity as a result of the said ratio of titanium to aluminum.

References Cited in the file of this patent UNITED STATES PATENTS Darmara Oct. 8, 1957 Bieber et al Nov. 10, 1959 Bieber Mar. 28, 1961 Gittus Nov. 20, 1962 Gittus Oct. 22, 1963 FOREIGN PATENTS Great Britain Sept. 21, 1955 Great Britain May 27, 1959 

1. A CAST ALLOY HAVING GOOD STRESS-RUPTURE CHARACTERISTICS AT TEMPERATURES IN THE RANGE OF ABOUT 815*C. TO ABOUT 1020*C. AND EXHIBITING SUBSTANTIALLY ENHANCED CHARACTERISTICS OF UNIDORMITY AND REPRODUCIBILITY OVER THE SAID TEMPERATURE RANGE, SAID ALLOY CONSISTING, BY WEIGHT, OF ABOUT 13% TO ABOUT 20% CHROMIUM, ABOUT 3% TO ABOUT 7% COBALT, ABOUT 3% TO ABOUT 7% MOLYBDENUM, ABOUT 1.0% TO ABOUT 2.8% TITANIUM, ABOUT 4.7% TO ABOUT 7.5% ALUMINUM, THE SUM OF THE TITANIUM AND ALUMINUM BEING ABOUT 7% TO 9% AND BEING SO CORRELATED THAT THE RATIO OF THE TITANIUM PERCENTAGE TO THE ALUMINUM PERCENTAGE IS NOT GREATER THAN 0.4, ABOUT 0.05% TO ABOUT 0.25% CARBON, ABOUT 0.003% TO ABOUT 0.03% BORON, ABOUT 0.02% TO ABOUT 0.07% ZIRCONIUM AND THE BALANCE BEING ESSENTIALLY NICKEL, SAID CAST ALLOY BEING FURTHER CHARACTERIZED BY A LESSER INCIDENCE OF SHRINKAGE POROSITY AS A RESULT OF THE SAID RATIO OF TITANIUM TO ALUMINUM. 